Tech Notes

Tool to Improve Ion-Channel Screening

Instrument Seeks to Advance Ligand-Gated Aspect of Critically Important Field

The first decade of the 21st century has delivered an extraordinary range of new technologies with relevance to early-stage ion-channel drug discovery research. The advances have been at such a pace that only ten years ago the options for evaluating compound interactions with ion channels were broadly limited to efflux and fluorescence-based high-throughput screening assays, with conventional electrophysiology reserved for more detailed evaluation of priority compounds.

Planar substrate electrophysiology techniques then started to enable compound screening against voltage-gated and slow ligand-gated ion channels. Subsequent developments in instrumentation technology have now made it possible to facilitate the application of relatively complex voltage protocols to screen up to 100,000 compounds for voltage-gated ion-channel targets.

Although voltage-gated ion-channel research has been relatively well served in terms of instrumentation, the ligand-gated ion-channel field has advanced at a slower pace. This situation has recently been resolved and a range of suitable automated electrophysiology instruments are now available, among them the Dynaflow® HT, launched by Cellectricon earlier this year. BioFocus has chosen Cellectricon as its partner of choice for ligand-gated ion-channel screening technology.

Each Dynaflow HT system combines fully automated 96-well whole-cell patch-clamp recording, with a custom-designed microfluidics-based consumable plate, which facilitates control over the length of time that ligands and compounds are perfused over cells. This instrument enables recordings to be taken with continuous voltage-clamp being applied throughout an experiment, providing control of cell membrane potential during each assay as well as enabling the creation of customized voltage step protocols for both voltage- and ligand-gated ion-channel targets.

The consumable plate has been specifically designed to be economical to manufacture and is based upon disposable chips formed from a molded polydimethylsiloxane microfluidic network bonded to a glass substrate. This molded network design brings down the cost per data point, although it does mean that seal resistance for whole-cell recordings is generally around 100 MΩ.

As a result, the system amplifiers have been specifically designed to record with mega ohm seals with automatic series resistance and capacitance compensation enhancing the recording fidelity. The plate only requires low volumes of fluids such as cells in suspension and compounds; for example, only 5 µL of a cell suspension with a density as low as 100,000 cells per mL is required to run each experiment.

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